Rcm1 and shower pump not turning on

[pghstochaj]

Hi,

I am looking for some advice please.

We have a vented hot water system with a salamander water pump on the hot water system. It works fine when the taps are used but it doesn't come on automatically when you use the shower (which is connected to the pumped hot water system and mains cold) - presumably the pressure drop through the thermostatic shower valve is too much to get a flow sufficient to turn on the shower pump?

We have managed with this until now by blipping the hot water tap and this fires the pump into life and therefore the shower. However, at the time of the initial problem we bought a RCM1 negative head system on our plumber's advice just didn't fit it.

A plumber is coming in tomorrow to do various bits of work and I asked him to take a look at it but he suggested it wouldn't work but didn't understand what the RCM1 does.

Is he right or do you think the RCM1 is correct for this situation? Are there alternative fixes to this? The plumber who fitted the pump has already maximised the flow of hot to the pump (larger pipework, increased height of the tank etc.)

Thanks in advance,
Paul

 

[DrPlumb]

Where is the pump installed? Where is the cylinder in relation to the shower? Ie cylinder downstairs, shower up..... The shower should be fully pumped hot and cold, not pumped hot and mains cold....they require balanced pressure across the hot and cold, might be worth checking this out first before you start getting people to make costly changes to the system. I'm assuming the pump isn't pumping the mains cold? Well, I would hope not!

 

[pghstochaj]

Hi,

The shower is upstairs, the hot water tank is at a similar level and the only pressure on it is from the cold water tank in the loft. The shower is pumped hot and mains cold. I know they should be balanced but they aren't, my understanding was that the rcm1 would deal with that.

I was hoping to avoid buying a new twin impeller pump and I prefer to use mains as my cold water tank isn't huge.

Thanks
Paul

 

[hazetimesfive]

i would expect that this problem is caused by the mains cold water, theory might say that the neg head kit would fix this but it is only that.

unbalanced supplies are always troublesome.

 

[DrPlumb]

Ok well it's up to u, it's not correct tho. If you spent out on the rcm1 so may as well bought a twin impeller pump and done it properly....

I can see your point re: the size of the tank but, if it's that small it may even be too small for the pump you have?

You asked for advice, you have it, scrap the mains feed, it shouldn't need a negative head kit if its done properly.

Another thought.....how is the hot water feed to the pump taken off the cylinder? This is important too.